Lubricating oil additives

ABSTRACT

A lubricating oil composition comprising at least 50 percent by mass, based on the mass of the composition of an oil of lubricating viscosity and 0.01 to 25 percent by mass, based on the mass of the composition of a polymer comprising units (a) and one or both units (b) and (c):
 
—N(COR 1 )(CH 2 ) x —  (a)
 
—NH(CH 2 ) y —  (b)
 
—N(CH 2 CH 2-k (CH 3 ) k COOR 2 )(CH 2 ) z    (c)
         where the total number (n) of units (a), (b) and (c) is an integer between 4 and 500; wherein x, y and z are independently 2 or 3; wherein k is zero or 1. The polymer shows good solubility in the lubricating oil and provides friction modification. A method of synthesising a polymer is also disclosed.

FIELD OF THE INVENTION

This invention relates to lubricating oil compositions containing polymeric additives useful for example, to lubricate the crankcase of spark-ignited or compression-ignited internal combustion engines. More especially, the additives provide friction modifying properties to lubricating oils and are polymers containing units which are derived from oxazoline monomers or oxazine monomers. The polymers also have good solubility in base oils and do not have an adverse effect on lubricant viscosity.

BACKGROUND OF THE INVENTION

There is much interest in improving the fuel economy of gasoline and diesel engines. This can be done, through the lubricant engine oil, by reducing the friction contribution either of the bulk fluid (by lowering the oil viscosity) or improving the friction of the contacting parts by inclusion of friction modifier additives.

There is therefore interest in additives with low friction properties in low viscosity oils.

It is also important that additives used in lubricating oils have good solubility, in order for the oils to remain stable under prolonged storage.

Dispersant viscosity modifier (DVM) additives are known to provide friction modification Examples known in the art, based on polymer technology, are olefin copolymers (OCP) and methacrylate copolymers. A problem with such additives especially in applications which require ultra-low viscosity lubricating fluids such as 0W-8, 0W-16, 0W-20 is their high thickening efficiencies.

Poly(2-oxazoline)s are known in the art. For example, the art describes the living cationic ring-opening polymerization of 2-oxazolines. See Hoogenboom et al., Angew. Chem. Int. Ed 2009, 48, 7978-7994. U.S. Pat. No. 4,120,804 describes the use of short oligomers of poly(2-oxazoline)s having 2 to 15 repeating units as dispersants to prevent or reduce the formation of sludges, or to neutralise acidic components etc. in lubricating oils. The polymerisation initiator is a polymeric material of molecular weight equal to or greater than 250 and the oxazoline is 2-substituted with a hydrocarbyl group of 1-18 carbon atoms. No mention is made of friction modification, or of lubricant viscosity impact.

Polyoxazines are also known in the art see Hoogenboom et al., Macromol., 2011, 3420. U.S. Pat. No. 4,001,147 describes certain polyoxazines as useful to remove phenolic compounds from aqueous waste streams.

U.S. Pat. No. 5,439,978 describes the use of both oxazoline and oxazine-based copolymers as additives to render electrically conductive, nonconductive materials such as plastics.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a lubricating oil composition comprising at least 50 percent by mass, based on the mass of the composition of an oil of lubricating viscosity and 0.01 to 25 percent by mass, based on the mass of the composition of a polymer comprising units (a) and one or both units (b) and (c): —N(COR¹)(CH₂)_(x)—  (a) —NH(CH₂)_(y)—  (b) —N(CH₂CH_(2-k)(CH₃)_(k)COOR²)(CH₂)_(z)   (c)

wherein the total number (n) of units (a), (b) and (c) is an integer between 4 and 500; wherein x, y and z are independently 2 or 3; wherein k is zero or 1;

wherein the polymer carries an inorganic or organic nucleophilic polymerisation terminating group (t), and an initiator group (i) connected to the N atom of a unit (a), (b) or (c), the initiator group (1) being effective to initiate the polymerisation of linear, branched or cyclic hydrocarbyl moieties;

wherein R¹ comprises a single or a mixture of linear, branched or cyclic hydrocarbyl groups having 1-50 carbon atoms, some or all having 12-50 carbon atoms, or of at least one macro-monomeric hydrocarbyl group with more than 50 carbon atoms; and

wherein R² comprises a substituted or unsubstituted hydrocarbyl group having 1 to 30 carbon atoms, which group may be, linear or branched or cyclic, saturated or unsaturated, or aromatic.

In preferred embodiments, group R² is a substituted hydrocarbyl group which may carry one or more hetero atoms, functional groups or has been modified by reaction with other moieties. This enables the polymer to be provided with chemical and/or physical properties which may provide additional benefits when used in lubricating oil compositions. Some non-limiting examples of suitable groups R² will be apparent from the descriptions hereinbelow.

In a second aspect, the invention provides a method of lubricating the crankcase of an internal combustion engine comprising operating the engine and lubricating the crankcase with a lubricating composition of the first aspect of the invention in the faun of a crankcase lubricant.

In a third aspect, the invention provides the use of a polymer comprising units (a) and one or both units (b) and (c): —N(COR¹)(CH₂)_(x)—  (a) —NH(CH₂)_(y)—  (b) —N(CH₂CH_(2-k)(CH₃)_(k)COOR²)(CH₂)_(z)   (c)

wherein the total number (n) of units (a), (b) and (c) is an integer between 4 and 500; wherein x, y and z are independently 2 or 3; wherein k is zero or 1;

wherein the polymer carries an inorganic or organic nucleophilic polymerisation terminating group (t), and an initiator group (i) connected to the N atom of a unit (a), (b) or (c), the initiator group (i) being effective to initiate the polymerisation of linear, branched or cyclic hydrocarbyl moieties;

-   -   wherein R¹ comprises a single or a mixture of linear, branched         or cyclic hydrocarbyl groups having 1-50 carbon atoms, some or         all having 12-50 carbon atoms, or of at least one         macro-monomeric hydrocarbyl group with more than 50 carbon         atoms; and

wherein R² comprises a substituted or unsubstituted hydrocarbyl group having 1 to 30 carbon atoms, which group may be, linear or branched or cyclic, saturated or unsaturated, or aromatic, in a lubricating oil composition for an internal combustion engine to provide the lubricating oil composition, in operation of the engine, with friction reducing properties.

As described in EP 3257921 A1 and co-pending applications EP 18199179.5, EP 18203212.8 and EP 18199804.8, units (a), (b) and (c) of the polymer may be derived from 2-substituted-2-oxazoline monomers, in the case where x, y or z are equal to 2, or from 2-substituted-2-oxazine monomers, in the case where x, y or z are equal to 3. When mixtures of 2-substituted-2-oxazoline monomers and 2-substituted-2-oxazine monomers are used, the values for x, y and z will be 2 in some cases and 3 in others

As described in more detail hereinbelow, the polymer may be prepared by first polymerising one or more 2-substituted-2-oxazoline monomers, one or more 2-substituted-2-oxazine monomers, or a mixture of one or more 2-substituted-2-oxazoline monomers and one or more 2-substituted-2-oxazine monomers, for example by living cationic ring-opening polymerization, to form a polymer comprising only units (a). Subsequent partial hydrolysis can then be used to convert some units (a) into units (b). Units (b) can then be converted by reaction with an acrylate or methacrylate species to introduce units (c) into the polymer, which may be further reacted to introduce additional functionality. Several embodiments are possible, for example the step to convert units (b) into units (c) may be omitted such that the polymer comprises units (a) and (b) but not (c). Alternatively, some units (b) may be converted into units (c) such that the polymer comprises units (a), (b) and (c). Further alternatively, all units (b) may be converted into units (c) such that the polymer comprises units (a) and (c) but not (b).

The relative proportions of units (a), (b) and (c) in the polymer may be any suitable values and will be determined by both the extent of hydrolysis and the subsequent extent of further reaction to produce units (c), if present. In embodiments where units (c) are not present, the polymer may contain up to 60 mol %, preferably up to 50, 40, 30 25, 20 or 10 mol % of units (b). Similarly, where units (b) are not present, the polymer may contain up to 60 mol %, preferably up to 50, 40, 30 25, 20 or 10 mol % of units (c). In embodiments where units (a), (b) and (c) are present, the polymer may contain up to 60 mol %, preferably up to 50, 40, 30 25, 20 or 10 mol % of units (b) and (c) combined, where the molar ratio of units (b): units (c) ranges from 1:10 to 10:1, preferably from 1:5 to 5:1, for example 1:2 to 2:1.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

In this specification, the following words and expressions, if and when used, have the meaning given below:

“active ingredients” or “(a.i.)” refers to additive material that is not diluent or solvent;

“comprising” or any cognate word specifies the presence of stated features, steps, or integers or components, but does not preclude the presence or addition of one or more other features, steps, integers, components or groups thereof. The expressions “consists of” or “consists essentially of” or cognates may be embraced within “comprises” or any cognate word. The expression “consists essentially of” permits inclusion of substances not materially affecting the characteristics of the composition to which it applies. The expression “consists of” or cognates means only the stated features, steps, integers components or groups thereof are present to which the expression refers;

“hydrocarbyl” means a chemical group of a compound that contains hydrogen and carbon atoms and that is bonded to the remainder of the compound directly via a carbon atom. The use of the qualifier “substituted” means that the hydrocarbyl group may contain one or more atoms other than carbon and hydrogen (“hetero atoms”). Those skilled in the art will be aware of suitable groups (e.g., halo, especially chloro and fluoro, amino, allcoxyl, carboxy, ester, mercapto, alkylmercapto, nitro, nitroso, sulfoxy, etc.). The group may be unsaturated, and/or may be polymeric;

“oil-soluble” or “oil-dispersible”, or cognate terms, used herein do not necessarily indicate that the compounds or additives are soluble, dissolvable, miscible, or are capable of being suspended in the oil in all proportions. These do mean, however, that they are, for example, soluble or stably dispersible in oil to an extent sufficient to exert their intended effect in the environment in which the oil is employed. Moreover, the additional incorporation of other additives may also permit incorporation of higher levels of a particular additive, if desired;

-   -   “ashless” in relation to an additive means the additive does not         include a metal;     -   “ash-containing” in relation to an additive means the additive         includes a metal;     -   “major amount” means in excess of 50 mass % of a composition or         mixture;     -   “minor amount” means 50 mass % or less of a composition or         mixture;     -   “effective amount” in respect of an additive means an amount of         such an additive in the composition (e.g. an additive         concentrate) that is effective to provide, and provides, the         desired technical effect;     -   “ppm” means parts per million by mass, based on the total mass         of the composition;     -   “metal content” of a composition or of an additive component,         for example molybdenum content or total metal content of the         additive concentrate (i.e. the sum of all individual metal         contents), is measured by ASTM D5185;     -   “TBN” in relation to an additive component or of a composition,         means total base number (mg KOH/g) as measured by ASTM 1J2896;     -   “KV₁₀₀” means kinematic viscosity at 100° C. as measured by ASTM         D445; HTHS means High Temperature High Shear at 150° C. as         measured by—CEC-L-36-A-90.     -   “phosphorus content” is measured by ASTM D5185;     -   “sulfur content” is measured by ASTM D2622;     -   “sulfated ash content” is measured by ASTM D874;     -   M_(n) means number average molecular weight as measured by Gel         Permeation Chromatography with reference to linear narrow         poly(methylmethacrylate) standards in the range of 550 to         600,000 g/mol;     -   M_(w) means weight average molecular weight as measured by Gel         Permeation Chromatography with reference to linear narrow         poly(methylmethacrylate) standards in the range of 550 to         600,000 g/mol;     -   “dispersity” means M_(w)/M_(n), (denoted by Ð)

Also, it will be understood that various components used, essential as well as optimal and customary, may react under condition of formulation, storage and use and that the invention also provides the product(s) obtainable or obtained by any such reaction.

Further it is understood that any upper and lower quality, range or ratio limits set forth herein may be independently combined.

Polymers

As discussed above, the polymers useful in the present invention may be made in a stepwise manner.

In a first step, a polymer is formed having only units (a). This polymer may be a homopolymer or a copolymer. A homopolymer may be formed by polymerising one or more 2-substituted-2-oxazoline monomers or one or more 2-substituted-2-oxazine monomers. It will be understood that a homopolymer in this context means that only one type or class of monomer is used, i.e. either an oxazoline or an oxazine, and not necessarily that each monomer used is identical (c.f. polyethylene as an example). Polymers which are obtained from a mixture of the same type or class of monomer, for example two or more different 2-substituted-2-oxazoline monomers or two or more different 2-substituted-2-oxazine monomers, are intended to be captured under the description of homopolymer.

Copolymers having only units (a) may be formed by polymerising one or more 2-substituted-2-oxazoline monomers and one or more 2-substituted-2-oxazine monomers. In this case, as is known in the art, the copolymers may be of different types. As examples of copolymers there may be mentioned statistical copolymers which are formed where the polymerisation follows a known statistical rule, for example Bernouillian statistics or Markovian statistics. A statistical copolymer where the probability of finding a particular type of monomer residue at any particular point in the polymer chain is independent of the types of surrounding monomers can be referred to as a random copolymer. Statistical and random copolymers may be distinguished from more ordered copolymer types such as alternating copolymers, periodic copolymers and block copolymers. Block copolymers, i.e. in which two or more polymer sub-units are linked by covalent bonds (e.g. as di- or tri-blocks) may be used. The blocks in any block copolymer may be of equal size or of different sizes and the architecture of the copolymers can vary. For example, block copolymers may have only a single block of each monomer (i.e. in a ‘AB’ arrangement) or multiple blocks of each monomer (i.e. in an ‘ABABAB..’ arrangement) where blocks ‘A’ and ‘B’ may be the same size or of different sizes

Also noteworthy are branched copolymers, in particular star polymers where several (three or more) linear polymer chains (or “arms”) are covalently bonded to a central core.

The polymer (or copolymer) having only units (a) is conveniently formed by polymerising 2-substituted-2-oxazoline monomers and/or 2-substituted-2-oxazine monomers with an initiator and subsequently terminating polymerisation. Any cationic species is capable of initiating polymerization of 2-oxazolines or 2-oxazines. Examples include H⁺ (from HCl or other acids); R⁺ (for example from alkyl halides such as RI or RBr); and metal cations and salts (e.g. Zr⁴⁺). Any nucleophilic species is capable of terminating the polymerization (e.g. OH⁻ from atmospheric water, OTs⁻(tosylate), H₂NR, HSR). Other suitable initiator groups (i) and terminating groups (t) will be known to those skilled in the art. Multifunctional initiators or terminators, cross linking or coupling can be employed to provide star architectures.

In a second step, the polymer having only units (a) is partially hydrolysed to convert some units (a) into units (b). Hydrolysis of such polymers is facile and suitable techniques and methods will be known to those skilled in the art. One preferred method is to treat the polymer with a mixture of aqueous hydrochloric acid and THF but other options would include reaction under basic conditions using aqueous sodium hydroxide or methanolic sodium hydroxide in mixture with a suitable solvent. It is important in the context of the present invention that not all units (a) are converted to repeat units (b), that is, full hydrolysis should be avoided. As discussed above, any degree of partial hydrolysis is possible however in embodiments, hydrolysis yields a polymer containing up to 60 mol %, preferably up to 50, 40, 30 25, 20 or 10 mol % of units (b).

In one embodiment, the polymer obtained from the second step is not reacted any further. Preferably however, in another embodiment, the polymer is further reacted in a third step to convert some or all of the units (b) into units (c), Preferably in this third step, a Michael addition reaction is performed whereby the polymer from the second step is reacted with an acrylate or methacrylate species. Any acrylate or methacrylate species may be used however a species which facilitates further reaction or functionalisation is preferred. Acrylates are preferred over methacrylates. It will be understood that in the structure given for units (c), when an acrylate is used, the value k is zero and when a methacrylate is used, k is equal to 1. A preferred species is propargyl acrylate (prop-2-yn-1-yl-acrylate).

In the preferred embodiment where the polymer comprises units (c), preferably R² comprises an alkynyl group of the structure —(CH₂)_(m)CCH, where m is an integer from 1 to 10. Preferably m is 1 such that R² is prop-1-ynyl. In this case, units (c) will have a structure (I):

Further examples are analogous structures (I) where R² is an alk-1-ynyl group with more carbon atoms than prop-1-ynyl, i.e., m>1.

The terminal alkynyl group in structure (I) above permits further reaction to produce units (c) where R² is a substituted hydrocarbyl group.

In a preferred embodiment, R² comprises a hydrocarbyl group terminally substituted by a 1,2,3-triazole group. Preferably, the 1,2,3-triazole group is substituted with a hydrocarbyl group having 1 to 50 carbon atoms, preferably 1 to 30 carbon atoms. Preferably, polymers comprising units (c) which have structure (I) are further reacted with an azide, for example an alkyl azide. An azide-alkyne “click” reaction can be used to produce units (c) having structure (II):

where R³ is preferably a hydrocarbyl group or a substituted hydrocarbyl group having 1 to 50 carbon atoms, more preferably a hydrocarbyl group or a substituted hydrocarbyl group having 1 to 30 carbon atoms. Preferably, R³ is a substituted hydrocarbyl group.

In another preferred embodiment, R² comprises a hydrocarbyl group terminally substituted by one or more thioether groups. Preferably, polymers comprising units (c) which have structure (I) are further reacted with a thiol, for example a primary alkylthiol. A thiol-yne “click” reaction can be used to produce units (c) having structures (III):

where preferably R⁴ and R⁵ are independently hydrocarbyl groups or substituted hydrocarbyl groups having 1 to 50 carbon atoms, more preferably hydrocarbyl groups or substituted hydrocarbyl groups having 1 to 30 carbon atoms. Preferably R⁴ and R⁵ are independently substituted hydrocarbyl groups.

Preferably, the total number (n) of units (a), (b) and (c) in the polymer is from 10 to 300, preferably 25 to 300, more preferably 25 to 100.

Preferably, the polymer has a number average molecular weight (Mn) of 2,000-500,000 g/mol. More preferably, the polymer has a number average molecular weight (Mn) of 4,000-100,000 g/moL Even more preferably, the polymer has a number average molecular weight (Mn) of 6,000-50,000 g/mol, for example 8,000-20,000 g/mol. All molecular weights are as measured by Gel Permeation Chromatography with reference to linear narrow poly(methylmethacrylate) standards in the range of 550 to 600,000 g/mol.

In an embodiment, the copolymer has a star architecture with three or more arms, and a number average molecular weight (Mn) of 10,000-500,000 g/mol, R¹ and/or R² having at least some groups of 12-50 carbon atoms in at least one arm. All molecular weights are as measured by Gel Permeation Chromatography with reference to linear narrow poly(methylmethacrylate) standards in the range of 550 to 600,000 g/mol.

When R¹ is a macro-monomeric hydrocarbyl group, it may be provided via

-   -   a) polymerization from a reactive group in an R¹ precursor; or     -   b) incorporation of a pre-formed macro-monomeric in hydrocarbyl         group in an R¹ precursor.

The significance of the presence of R¹ groups having 12-50 carbon atoms is to make the copolymers sufficiently oleophilic to confer solubility in a polar media such as base oil.

Preferably R¹ contains 1 to 36, more preferably 1 to 20 carbon atoms, provided that some or all of the groups R¹ have 12 to 75, preferably 12 to 50, for example 12 to 36 carbon atoms.

As examples of the number of carbon atoms in W, there may be mentioned 1, 2, 8, 12, 17 and 24.

In a preferred embodiment R¹ comprises unsaturated hydrocarbyl groups having between 8 and 20 carbon atoms.

Preferably, at least 5% of the total number of groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having between 8 and 20 carbon atoms. More preferably, at least 10%, or 20% or 30% or 40% or 50% of the total number of groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having between 8 and 20 carbon atoms. Most preferably, at least 60% or 70% of the total number of groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having between 8 and 20 carbon atoms.

Preferably, at least 5% of the total number of groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having between 15 and 20 carbon atoms. More preferably, at least 10%, or 20% or 30% or 40% or 50% of the total number of either or groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having between 15 and 20 carbon atoms. Most preferably, at least 60% or 70% of the total number of groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having between 15 and 20 carbon atoms.

Preferably, at least 5% of the total number of groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having 17 carbon atoms. More preferably, at least 10%, or 20% or 30% or 40% or 50% or 60% of the total number of groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having 17 carbon atoms. Even more preferably, at least 70% of the total number of groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having 17 carbon atoms.

In an embodiment, groups R¹ do not contain any hetero-atoms, i.e. are hydrocarbon groups. Preferably groups R¹ are hydrocarbon groups.

In preferred embodiments, at least 50% of the total number of groups R¹ in the polymer comprise singly, doubly or triply-unsaturated C₁₇ alkenyl groups or any mixture thereof. More preferably, at least 60% of the total number of groups R¹ in the polymer comprise singly, doubly or triply-unsaturated C₁₇ alkenyl groups or any mixture thereof. Even more preferably, at least 70% of the total number of groups R¹ in the polymer comprise singly, doubly or triply-unsaturated C₁₇ alkenyl groups or any mixture thereof.

In particularly preferred embodiments, groups R¹ comprise a mixture of singly, doubly or triply-unsaturated C₁₇ alkenyl groups which mixture predominates in singly, and doubly-unsaturated C₁₇ alkenyl groups. Such mixtures may comprise small amounts of smaller and longer molecules.

Suitable sources for mixtures of groups for R¹ include 2-oxazolines and 2-oxazines derived from natural fatty acids such as tall oil fatty acid (TOFA) and rape-seed oil fatty acid. Other suitable sources will be known to those skilled in the art.

In an embodiment, R¹ may contain hetero atoms (such as N, O, S, P, B, Si, F, Cl, Br, I). As discussed hereinabove, the term ‘hydrocarbyl’ when applied to R¹ (and R²) permits the presence of a limited number of hetero atoms and so is not limited to groups which contain carbon and hydrogen only.

The synthesis of the polymer forms another aspect of the present invention and so in a fourth aspect, there is provided a method for synthesising a polymer, the method comprising:

-   -   (i) polymerising one or more 2-substituted-2-oxazoline monomers,         one or more 2-substituted-2-oxazine monomers, or a mixture         thereof in the presence of an initiator;     -   (ii) partially hydrolysing the product formed in step (i); and,     -   (iii) performing a Michael addition reaction to react one or         more acrylate or methacrylate species with the product of step         (ii).

In a preferred embodiment in step (iii), the Michael addition reaction reacts an alk-2-yn-1-yl-acrylate species with the product of step (ii).

In a more preferred embodiment, in a further step (iv), the product of step (iii) is reacted with an alkyl azide or a primary alkyl thiol. Preferably, the alk-2-yn-1-yl-acrylate species is prop-2-yn-1-yl-acrylate (propargyl acrylate).

Lubricating Compositions

Lubricating compositions of the invention may be lubricants suitable for use as motor vehicle motor oils comprising a major amount of oil of lubricating viscosity and minor amounts of performance-enhancing additives, including the polymeric material. The lubricating composition may also be in the form of an additive concentrate for blending with oil of lubricating viscosity to make a final lubricant.

Preferably the lubricating compositions of the invention will contain 0.01 to 25 percent by mass, based on the mass of the composition of the polymer, more preferably 0.01 to 10, for example up to 0.5, 1, 2, 3, 4 or 5 percent by mass, based on the mass of the composition. When in the form of an additive concentrate, typically the polymer will be present in an oil of lubricating viscosity in an amount of 30 to 50 percent by mass, based on the mass of the composition.

The oil of lubricating viscosity (sometimes referred to as “base stock” or “base oil”) is the primary liquid constituent of a lubricant, into which additives and possibly other oils are blended, for example to produce a final lubricant (or lubricant composition). A base oil, which is useful for making additive concentrates as well as for making lubricating oil compositions therefrom, may be selected from natural oils (vegetable, animal or mineral) and synthetic lubricating oils and mixtures thereof.

Definitions for the base stocks and base oils in this invention are the same as those found in the American Petroleum Institute (API) publication “Engine Oil Licensing and Certification System”, Industry Services Department, Fourteenth Edition, December 1996, Addendum 1, December 1998, which categorizes base stocks as follows:

-   -   a) Group I base stocks contain less than 90 percent saturates         and/or greater than 0.03 percent sulphur and have a viscosity         index greater than or equal to 80 and less than 120 using the         test methods specified in Table E-1.     -   b) Group II base stocks contain greater than or equal to 90         percent saturates and less than or equal to 0.03 percent sulphur         and have a viscosity index greater than or equal to 80 and less         than 120 using the test methods specified in Table E-1.     -   c) Group III base stocks contain greater than or equal to 90         percent saturates and less than or equal to 0.03 percent sulphur         and have a viscosity index greater than or equal to 120 using         the test methods specified in Table E-1.     -   d) Group IV base stocks are polyalphaolefins (PAO).     -   e) Group V base stocks include all other base stocks not         included in Group I, II, III, or IV.

Typically, the base stock has a viscosity preferably of 3-12, more preferably 4-10, most preferably 4.5-8, mm²/s at 100° C.

TABLE E-1 Analytical Methods for Base Stock Property Test Method Saturates ASTM D 2007 Viscosity Index ASTM D 2270 Sulphur ASTM D 2622 ASTM D 4294 ASTM D 4927 ASTM D 3120

Preferably, the oil of lubricating viscosity comprises greater than or equal to 10, more preferably greater than or equal to 20, even more preferably greater than or equal to 25, even more preferably greater than or equal to 30, even more preferably greater than or equal to 40, even more preferably greater than or equal to 45, mass % of a Group II or Group III base stock, based on the total mass of the oil of lubricating viscosity. Even more preferably, the oil of lubricating viscosity comprises greater than 50, preferably greater than or equal to 60, more preferably greater than or equal to 70, even more preferably greater than or equal to 80, even more preferably greater than or equal to 90, mass % of a Group II or Group III base stock, based on the total mass of the oil of lubricating viscosity. Most preferably, the oil of lubricating viscosity consists essentially of a Group II and/or Group III base stock. In some embodiments the oil of lubricating viscosity consists solely of Group II and/or Group III base stock. In the latter case it is acknowledged that additives included in the lubricating oil composition may comprise a carrier oil which is not a Group II or Group III base stock.

Other oils of lubricating viscosity that may be included in the lubricating oil composition are detailed as follows:

Natural oils include animal and vegetable oils (e.g. castor and lard oil), liquid petroleum oils and hydro refined, solvent-treated mineral lubricating oils of the paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of lubricating viscosity derived from coal or shale are also useful base oils.

Synthetic lubricating oils include hydrocarbon oils such as polymerized and interpolymerized olefins (e.g. polybutylenes, polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes), poly(1-decenes)); alkylbenzenes (e.g. dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes); polyphenols (e.g. biphenyls, terphenyls, alkylated polyphenols); and alkylated diphenyl ethers and alkylated diphenyl sulfides and the derivatives, analogues and homologues thereof.

Another suitable class of synthetic lubricating oil comprises the esters of dicarboxylic acids (e.g. phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebasic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkylinalonic acids, alkenyl malonic acids) with a variety of alcohols (e.g. butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol). Specific examples of these esters include dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, and the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid.

Esters useful as synthetic oils also include those made from C₅ to C₁₂ monocarboxylic acids and polyols, and polyol ethers such as neopentyl glycol, trimethyloipropane, pentaerythritol, dipentaerythritol and tripentaerythritol.

Unrefined, refined and re-refined oils can be used in the compositions of the present invention. Unrefined oils are those obtained directly from a natural or synthetic source without further purification treatment. For example, a shale oil obtained directly from retorting operations, a petroleum oil obtained directly from distillation or ester oil obtained directly from an esterification process and used without further treatment would be unrefined oil. Refined oils are similar to the unrefined oils except they have been further treated in one or more purification steps to improve one or more properties. Many such purification techniques, such as distillation, solvent extraction, acid or base extraction, filtration and percolation, are known to those skilled in the art. Re-refined oils are obtained by processes similar to those used to obtain refined oils applied to refined oils that have been already used in service. Such re-refined oils are also known as reclaimed or reprocessed oils and often are additionally processed by techniques for treating spent additive and oil breakdown products.

Other examples of base oil are gas-to-liquid (“GTL”) base oils, i.e. the base oil may be an oil derived from Fischer-Tropsch synthesised hydrocarbons made from synthesis gas containing H₂ and CO using a Fischer-Tropsch catalyst. These hydrocarbons typically require further processing in order to be useful as a base oil. For example, they may, by methods known in the art, be hydroisomerized; hydrocracked and hydroisomerized; dewaxed; or hydroisomerized and dewaxed.

The oil of lubricating viscosity may also comprise a Group I, Group IV or Group V base stocks or base oil blends of the aforementioned base stocks.

The lubricating compositions of the present invention preferably comprise at least 60% by weight, for example 70% by weight or more of an oil of lubricating viscosity, based on the weight of the composition.

Co-Additives

The lubricating oil compositions of all aspects of the present invention may further comprise one or more phosphorus-containing compounds; oxidation inhibitors or anti-oxidants; dispersants; metal detergents; and other co-additives, provided they are different from the polymer comprising units (a) and one or both units (b) and (c). These will be discussed in more detail below.

Suitable phosphorus-containing compounds include dihydrocarbyl dithiophosphate metal salts, which are frequently used as antiwear and antioxidant agents. The metal is preferably zinc, but may be an alkali or alkaline earth metal, or aluminium, lead, tin, molybdenum, manganese, nickel or copper. The zinc salts are most commonly used in lubricating oil in amounts of 0.1 to 10, preferably 0.2 to 2 mass %, based upon the total weight of the lubricating oil composition. They may be prepared in accordance with known techniques by first forming a dihydrocarbyl dithiophosphoric acid (DDPA), usually by reaction of one or more alcohol or a phenol with P₂S₅, and then neutralizing the formed DDPA with a zinc compound. For example, a dithiophosphoric acid may be made by reacting mixtures of primary and secondary alcohols. Alternatively, multiple dithiophosphoric acids can be prepared where the hydrocarbyl groups on one are entirely secondary in character and the hydrocarbyl groups on the others are entirely primary in character. To make the zinc salt, any basic or neutral zinc compound could be used but the oxides, hydroxides and carbonates are most generally employed. Commercial additives frequently contain an excess of zinc due to the use of an excess of the basic zinc compound in the neutralization reaction.

The preferred zinc dihydrocarbyl dithiophosphates are oil-soluble salts of dihydrocarbyl dithiophosphoric acids and may be represented by the following formula:

wherein R and R′ may be the same or different hydrocarbyl radicals containing from 1 to 18, preferably 2 to 12, carbon atoms and including radicals such as alkyl, alkenyl, aryl, arylalkyl, alkaryl and cycloaliphatic radicals. Particularly preferred as R and R′ groups are alkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, for example, be ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl, octadecyl, 2-ethyihexyl, phenyl, butylphenyl, cyclohexyl, methyleyclopentyl, propenyl, butenyl. In order to obtain oil solubility, the total number of carbon atoms (i.e. R and R′) in the dithiophosphoric acid will generally be 5 or greater. The zinc dihydrocarbyl dithiophosphate (ZDDP) can therefore comprise zinc dialkyl dithiophosphates. Lubricating oil compositions of the present invention suitably may have a phosphorus content of no greater than about 0.08 mass % (800 ppm). Preferably, in the practice of the present invention, ZDDP is used in an amount close or equal to the maximum amount allowed, preferably in an amount that provides a phosphorus content within 100 ppm of the maximum allowable amount of phosphorus. Thus, lubricating oil compositions useful in the practice of the present invention preferably contain ZDDP or other zinc-phosphorus compounds, in an amount introducing from 0.01 to 0.08 mass % of phosphorus, such as from 0.04 to 0.08 mass % of phosphorus, preferably, from 0.05 to 0.08 mass % of phosphorus, based on the total mass of the lubricating oil composition.

Oxidation inhibitors or antioxidants reduce the tendency of mineral oils to deteriorate in service. Oxidative deterioration can be evidenced by sludge in the lubricant, varnish-like deposits on the metal surfaces, and by viscosity growth. Such oxidation inhibitors include hindered phenols, alkaline earth metal salts of alkylphenolthioesters having preferably C₅ to C₁₂ alkyl side chains, calcium nonylphenol sulfide, oil soluble phenates and sulfurized phenates, phosphosulfurized or sulfurized hydrocarbons or esters, phosphorous esters, metal thiocarbamates, oil soluble copper compounds as described in U.S. Pat. No. 4,867,890, and is molybdenum-containing compounds.

Aromatic amines having at least two aromatic groups attached directly to the nitrogen constitute another class of compounds that is frequently used for antioxidancy. Typical oil-soluble aromatic amines having at least two aromatic groups attached directly to one amine nitrogen contain from 6 to 16 carbon atoms. The amines may contain more than two aromatic groups. Compounds having a total of at least three aromatic groups in which two aromatic groups are linked by a covalent bond or by an atom or group (e.g., an oxygen or sulfur atom, or a —CO—, —SO₂— or alkylene group) and two are directly attached to one amine nitrogen are also considered aromatic amines having at least two aromatic groups attached directly to the nitrogen. The aromatic rings are typically substituted by one or more substituents selected from alkyl, cycloalkyl, alkoxy, aryloxy, acyl, acylamino, hydroxy, and nitro groups. The amount of any such oil soluble aromatic amines having at least two aromatic groups attached directly to one amine nitrogen should preferably not exceed 0.4 mass %.

A dispersant is an additive whose primary function is to hold solid and liquid contaminations in suspension, thereby passivating them and reducing engine deposits at the same time as reducing sludge depositions. For example, a dispersant maintains in suspension oil-insoluble substances that result from oxidation during use of the lubricant, thus preventing sludge flocculation and precipitation or deposition on metal parts of the engine.

Dispersants in this invention are preferably “ashless”, as mentioned above, being non-metallic organic materials that form substantially no ash on combustion, in contrast to metal-containing and hence ash-forming materials, They comprise a long hydrocarbon chain with a polar head, the polarity being derived from inclusion of e.g. an O, P, or N atom, The hydrocarbon is an oleophilic group that confers oil-solubility, having, for example 40 to 500 carbon atoms. Thus, ashless dispersants may comprise an oil-soluble polymeric backbone.

A preferred class of olefin polymers is constituted by polybutenes, specifically polyisobutenes (PIS) or poly-n-butenes, such as may be prepared by polymerization of a C₄ refinery stream.

Dispersants include, for example, derivatives of long chain hydrocarbon-substituted carboxylic acids, examples being derivatives of high molecular weight hydrocarbyl-substituted succinic acid. A noteworthy group of dispersants is constituted by hydrocarbon-substituted succinimides, made, for example, by reacting the above acids (or derivatives) with a nitrogen-containing compound, advantageously a polyalkylene polyamine, such as a polyethylene polyamine. Particularly preferred are the reaction products of polyalkylene polyamines with alkenyl succinic anhydrides, such as described in U.S. Pat. Nos 3,202,678; 3,154,560; 3,172,892; 3,024,195; 3,024,237, 3,219,666; and 3,216,936, that may be post-treated to improve their properties, such as borated (as described in U.S. Pat. Nos. 3,087,936 and 3,254,025), fluorinated or oxylated. For example, boration may be accomplished by treating an acyl nitrogen-containing dispersant with a boron compound selected from boron oxide, boron halides, boron acids and esters of boron acids.

Preferably, the dispersant, if present, is a succinimide-dispersant derived from a polyisobutene of number average molecular weight in the range of 1000 to 3000, preferably 1500 to 2500, and of moderate functionality. The succinimide is preferably derived from highly reactive polyisobutene.

Another example of dispersant type that may be used is a linked aromatic compound such as described in EP-A-2 090 642.

A detergent is an additive that reduces formation of piston deposits, for example high-temperature varnish and lacquer deposits in engines; it normally has acid-neutralising properties and is capable of keeping finely-divided solids in suspension. Most detergents are based on metal “soaps”, that is metal salts of acidic organic compounds.

Detergents generally comprise a polar head with a long hydrophobic tail, the polar head comprising the metal salt of the acidic organic compound. The salts may contain a substantially stoichiometric amount of the metal when they are usually described as normal or neutral salts and would typically have a total base number or TBN at 100% active mass (as may be measured by ASTM D2896) of from 0 to 80. Large amounts of a metal base can be included by reaction of an excess of a metal compound, such as an oxide or hydroxide, with an acidic gas such as carbon dioxide.

The resulting overbased detergent comprises neutralised detergent as an outer layer of a metal base (e.g. carbonate) micelle. Such overbased detergents may have a TBN at 100% active mass of 150 or greater, and typically of from 200 to 500 or more.

Suitably, detergents that may be used include oil-soluble neutral and overbased sulfonates, phenates, sulfurised phenates, thiophosphonates, salicylates and naphthenates and other oil-soluble carboxylates of a metal, particularly alkali metal or alkaline earth metals, e.g. Na, K, Li, Ca and Mg. The most commonly-used metals are Ca and Mg, which may both be present in detergents used in lubricating compositions, and mixtures of Ca and/or Mg with Na. Detergents may be used in various combinations.

Additional additives may be incorporated into the compositions of the invention to enable particular performance requirements to be met. Examples of such additives which may be included in the lubricating oil compositions of the present invention are metal rust inhibitors, viscosity index improvers, corrosion inhibitors, oxidation inhibitors, other friction modifiers, anti-foaming agents, anti-wear agents and pour point depressants. Some are discussed in further detail below.

Friction modifiers and fuel economy agents that are compatible with the other ingredients of the final oil may also be included. Examples of such materials include glyceryl monoesters of higher fatty acids, for example, glyceryl mono-oleate; esters of long chain polycarboxylic acids with diols, for example, the butane diol ester of a dimerized unsaturated fatty acid; and alkoxylated alkyl-substituted mono-amines, diamines and alkyl ether amines, for example, ethoxylated tallow amine and ethoxylated tallow ether amine.

Other known friction modifiers comprise oil-soluble organo-molybdenum compounds. Such organo-molybdenum friction modifiers also provide antioxidant and antiwear credits to a lubricating oil composition. Examples of such oil-soluble organo-molybdenum compounds include dithiocarbamates, dithiophosphates, dithiophosphinates, xanthates, thioxanthates, sulfides, and the like, and mixtures thereof. Particularly preferred ate molybdenum dithiocarbamates, dialkyldithiophosphates, alkyl xanthates and alkylthioxanthates.

Additionally, the molybdenum compound may be an acidic molybdenum compound. These compounds will react with a basic nitrogen compound as measured by ASTM test D-664 or D-2896 titration procedure and are typically hexavalent. Included are molybdic acid, ammonium molybdate, sodium molybdate, potassium molybdate, and other alkali metal molybdates and other molybdenum salts, e.g., hydrogen sodium molybdate, MoOCl₄, MoO₂Br₂, Mo₂O₃Cl₆, molybdenum trioxide or similar acidic molybdenum compounds.

Among the molybdenum compounds useful in the compositions of this invention are organo-molybdenum compounds of the formula Mo(R″OCS₂)₄ and Mo(R″SCS₂)₄ wherein R″ is an organo group selected from the group consisting of alkyl, aryl, aralkyl and alkoxyalkyl, generally of from 1 to 30 carbon atoms, and preferably 2 to 12 carbon atoms and most preferably alkyl of 2 to 12 carbon atoms. Especially preferred are the dialkyldithiocarbamates of molybdenum.

Another group of organo-molybdenum compounds useful in the lubricating compositions of this invention are trinuclear molybdenum compounds, especially those of the formula Mo₃S_(k)L_(n)Q_(z) and mixtures thereof wherein the L are independently selected ligands having organo groups with a sufficient number of carbon atoms to render the compound soluble or dispersible in the oil, n is from 1 to 4, k varies from 4 to 7, Q is selected from the group of neutral electron donating compounds such as water, amines, alcohols, phosphines, and ethers, and z ranges from 0 to 5 and includes non-stoichiometric values. At least 21 carbon atoms should be present among all the ligand organo groups, such as at least 25, at least 30, or at least 35, carbon atoms.

Lubricating oil compositions useful in all aspects of the present invention preferably contain at least 10 ppm, at least 30 ppm, at least 40 ppm and more preferably at least 50 ppm molybdenum. Suitably, lubricating oil compositions useful in all aspects of the present invention contain no more than 1000 ppm, no more than 750 ppm or no more than 500 ppm of molybdenum. Lubricating oil compositions useful in all aspects of the present invention preferably contain from 10 to 1000, such as 30 to 750 or 40 to 500, ppm of molybdenum (measured as atoms of molybdenum).

The viscosity index of the base stock is increased, or improved, by incorporating therein certain polymeric materials that function as viscosity modifiers (VM) or viscosity index improvers (VII). Generally, polymeric materials useful as viscosity modifiers are those having number average molecular weights (Mn) of from 5,000 to 250,000, preferably from 15,000 to 200,000, more preferably from 20,000 to 150,000. These viscosity modifiers can be grafted with grafting materials such as, for example, maleic anhydride, and the grafted material can be reacted with, for example, amines, amides, nitrogen-containing heterocyclic compounds or alcohol, to form multifunctional viscosity modifiers (dispersant-viscosity modifiers).

Polymers prepared with diolefins will contain ethylenic unsaturation, and such polymers are preferably hydrogenated. When the polymer is hydrogenated, the hydrogenation may be accomplished using any of the techniques known in the prior art. For example, the hydrogenation may be accomplished such that both ethylenic and aromatic unsaturation is converted (saturated) using methods such as those taught, for example, in U.S. Pat. Nos. 3,113,986 and 3,700,633 or the hydrogenation may be accomplished selectively such that a significant portion of the ethylenic unsaturation is converted while little or no aromatic unsaturation is converted as taught, for example, in U.S. Pat. Nos. 3,634,595; 3,670,054; 3,700,633 and Re 27,145. Any of these methods can also be used to hydrogenate polymers containing only ethylenic unsaturation and which are free of aromatic unsaturation.

Pour point depressants (PPD), otherwise known as lube oil flow improvers (LOFIs) lower the lowest temperature at which the lube flows. Compared to VM, LOFIs generally have a lower number average molecular weight. Like VM, LOFIs can be grafted with grafting materials such as, for example, maleic anhydride, and the grafted material can be reacted with, for example, amines, amides, nitrogen-containing heterocyclic compounds or alcohol, to form multifunctional additives.

In the present invention it may be necessary to include an additive which maintains the stability of the viscosity of the blend. Thus, although polar group-containing additives achieve a suitably low viscosity in the pre-blending stage, it has been observed that some compositions increase in viscosity when stored for prolonged periods. Additives which are effective in controlling this viscosity increase include the long chain hydrocarbons functionalized by reaction with mono- or dicarboxylic acids or anhydrides which are used in the preparation of the ashless dispersants as hereinbefore disclosed.

When lubricating compositions contain one or more of the above-mentioned additives, each additive is typically blended into the base oil in an amount that enables the additive to provide its desired function. Representative effective amounts of such additives, when used in crankcase lubricants, are listed below. All the values listed (with the exception of detergent values since the detergents are used in the form of colloidal dispersants in an oil) are stated as mass percent active ingredient (A.I.).

MASS % MASS % ADDITIVE (Broad) (Preferred) Dispersant 0.1-20   1-8 Metal Detergents 0.1-15  0.2-9  Corrosion Inhibitor 0-5   0-1.5 Metal dihydrocarbyl dithiophosphate 0.1-6  0.1-4  Antioxidant 0-5 0.01-2.5 Pour Point Depressant 0.01-5   0.01-1.5 Antifoaming Agent 0-5 0.001-0.15 Supplemental Antiwear Agents  0-1.0   0-0.5 Friction Modifier 0-5   0-1.5 Viscosity Modifier 0.01-10  0.25-3  Base stock Balance Balance

Preferably, the Noack volatility of the fully formulated lubricating oil composition (oil of lubricating viscosity plus all additives) is no greater than 18, such as no greater than 14, preferably no greater than 10, mass %. Lubricating oil compositions useful in the practice of the present invention may have an overall sulfated ash content of from 0.5 to 2.0, such as from 0.7 to 1.4, preferably from 0.6 to 1.2, mass %.

It may be desirable, although not essential, to prepare one or more additive concentrates comprising additives (concentrates sometimes being referred to as additive packages) whereby several additives can be added simultaneously to the oil to form the lubricating oil composition.

EXAMPLES

The invention will now be particularly described in the following non-limiting examples.

Synthesis of Polymers

In a first step, a 2-substituted-2-oxazoline polymer is formed, The synthesis was as set out, for example, in EP 3 257 921 A1. A 2-substituted 2-oxazoline monomer, where the substituent was derived from a fatty acid containing a mixture of singly, doubly and triply-unsaturated Cr alkenyl groups (from rape-seed oil), was charged to a reaction flask and methyl tosylate was added in a monomer to initiator ratio of 50:1. This reaction mixture was stirred at 140° C. for 1 hour 10 minutes. The polymer had a number average molecular weight (Mn) of 10500 g/mol and a dispersity (Ð) of 1.36 as measured using GPC with narrow PMMA standards. The structure of the polymer was as follows:

In a second step, the polymer obtained in the first step was partially hydrolysed by treating with a 2:8 (v/v) mixture of 35% HCl(aq) and THF for 1 hour at 120° C. in a sealed vial in a microwave synthesiser. The resulting solution was precipitated in acetone, Then, the mixture was dissolved in THF and 4M NaOH was added until the pH was <9. The THF was removed in vacua, and the resulting precipitate filtered and washed with water. This produced a partially hydrolysed polymer having the structure:

In a third step, the polymer obtained in the second step was sealed into a vial with a THF solution of propargyl acrylate (3 eq) and trimethylamine (3 eq). The vial was placed into a microwave synthesiser and heated to 130° C. for 3 hours. The product was twice precipitated in slightly acidic methanol to remove the excess trimethylamine and propargyl acrylate. This promoted a Michael addition reaction to yield a polymer having the structure:

Two alternative fourth steps were then performed on the polymer obtained from the third step.

In one synthesis, the polymer was subjected to an azide alkyne “click” reaction by reacting it with hexadecyl azide in the presence of Cu(0) wire in THF at 50° C. overnight. The resultant polymer had the structure:

In another synthesis, the polymer from the third step was subjected to a thiol. yne “click” reaction by reacting it, in a sealed, degassed vial with dodecanethiol (2 eqs) in the presence of AIBN (25 mol %) in THF at 75° C. overnight. The resultant polymer had the structure:

Tests and Results

Two Example oils were prepared (amounts are expressed as weight proportions)

Reference Example 1 Example 2 Gp I base oil 100 99 99 Structure (II) where 1 R3 is 2-ethylhexyl Structure (II) where 1 R3 is hexadecyl Solubility

Examples 1 and 2 remained clear and bright and homogeneous for over four months after blending.

Viscosity

High Temperature High Shear (HTHS) viscosity measurements conducted at 150° C. demonstrate the very low viscomettic contribution of the examples of the invention compared to a Reference oil:

Reference Example 1 Example 2 HTHS150 (cPs) 1.80 1.84 1.81 Interfacial Tension

Measurements of interfacial tension were carried out on a Krüss DSA100 using the pendant drop method.

Both Examples provide significant reduction in interfacial tension relative to the Reference. This is indicative of surface activity which is desirable for wear protection.

Reference Example 1 Example 2 Equilibrated oil-in-water 33.3 10.04 10.69 interfacial tension Friction

Friction coefficients were measured on a PCS Instruments Mini Traction Machine (MTM) fitted with AISI 52100 steel substrates.

Both Examples demonstrate a reduction in friction over the base oil, which is indicative of surface activity and is desirable for fuel economy.

Reference Example 1 Example 2 Friction coefficient measured at 0.0893 0.0771 0.0812 135° C. and 20 mm/s rolling speed 

What is claimed is:
 1. A lubricating oil composition comprising at least 50 percent by mass, based on the mass of the composition, of an oil of lubricating viscosity and 0.01 to 25 percent by mass, based on the mass of the composition, of a polymer comprising units (a) and one or both units (b) and (c): —N(COR¹)(CH₂)_(x)—  (a) —NH(CH₂)_(y)—  (b) —N(CH₂CH_(2-k)(CH₃)_(k)COOR²)(CH₂)_(z)   (c) wherein the total number (n) of units (a), (b) and (c) is an integer between 4 and 500; wherein x, y and z are independently 2 or 3; wherein k is zero or 1; wherein the polymer carries an inorganic or organic nucleophilic polymerisation terminating group (t), and an initiator group (i) connected to the N atom of a unit (a), (b) or (c), the initiator group (i) being effective to initiate the polymerisation of linear, branched or cyclic hydrocarbyl moieties; wherein R¹ comprises: i) a single linear, branched or cyclic hydrocarbyl group having 12 to 50 carbon atoms; ii) a mixture of linear, branched or cyclic hydrocarbyl groups having 1 to 50 carbon atoms, where some or all of the hydrocarbyl groups have 12 to 50 carbon atoms; or iii) at least one macro-monomeric hydrocarbyl group with more than 50 carbon atoms; and wherein R² comprises a substituted or unsubstituted hydrocarbyl group having 1 to 30 carbon atoms, which group may be, linear or branched or cyclic, saturated or unsaturated, or aromatic.
 2. A lubricating oil composition according to claim 1, wherein R¹ comprises: i) a single linear, branched or cyclic hydrocarbyl group having 12 to 36 carbon atoms; or ii) a mixture of linear, branched or cyclic hydrocarbyl groups having 1 to 36 carbon atoms, where some or all of the hydrocarbyl groups have 12 to 36 carbon atoms.
 3. A lubricating oil composition according to claim 1, wherein at least 5% of the total number of the groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having between 8 and 20 carbon atoms.
 4. A lubricating oil composition according to claim 3, wherein at least 5% of the total number of the groups R¹ in the polymer comprise unsaturated hydrocarbyl groups having between 15 and 20 carbon atoms.
 5. A lubricating oil composition according to claim 1, wherein groups R¹ are obtained from natural fatty acids.
 6. A lubricating oil composition according to claim 5, wherein groups R¹ are obtained from tall oil fatty acid and/or rape-seed oil fatty acid.
 7. A lubricating oil composition according to claim 1, wherein R² is a group —(CH₂)_(m)CCH, where m is an integer from 1 to 10; a hydrocarbyl group terminally substituted by a 1,2,3-triazole group; or a hydrocarbyl group terminally substituted by one or more thioether groups.
 8. A lubricating oil composition according to claim 1, wherein the polymer does not comprise any units (c).
 9. A lubricating oil composition according to claim 1, wherein the polymer does not comprise any units (b).
 10. A lubricating oil composition according to claim 1, wherein n is from 10 to
 300. 11. A lubricating oil composition according to claim 10, wherein n is from 25 to
 100. 12. A lubricating oil composition according to claim 1, comprising one or more co-additives different from the polymer comprising units (a) and one or both units (b) and (c), the one or more co-additives being selected from one or more phosphorus-containing compounds; oxidation inhibitors or anti-oxidants; dispersants; metal-containing detergents; anti-wear agents; friction modifiers; and viscosity modifiers.
 13. A lubricating oil composition according to claim 1, comprising at least 70% by mass or more of an oil of lubricating viscosity, based on the mass of the composition.
 14. A method of lubricating the crankcase of an internal combustion engine comprising operating the engine and lubricating the crankcase with a lubricating oil composition according to claim
 1. 15. A lubricating oil composition according to claim 1, wherein the polymer is synthesized by a method comprising: (i) polymerising one or more 2-substituted-2-oxazoline monomers, one or more 2-substituted-2-oxazine monomers, or a mixture thereof in the presence of an initiator; (ii) partially hydrolysing the product formed in step (i); and, (iii) performing a Michael addition reaction to react one or more acrylate or methacrylate species with the product of step (ii).
 16. A lubricating oil composition according to claim 15, wherein in step (iii), the Michael addition reaction reacts an alk-2-yn-1 -yl-acrylate species with the product of step (ii).
 17. A lubricating oil composition according claim 16, further comprising a step (iv), where the product of step (iii) is reacted with an alkyl azide or a primary alkyl thiol. 